The present invention relates to an optical member, and a solid-state imaging device employing this optical member, and a manufacturing method thereof.
With solid-state imaging devices including CCD (Charge Coupled Device) and CMOS (Complementary Metal-oxide Semiconductor) sensors, it is common to provide an optical member such as an on-chip lens (OCL: On Chip Lens, also referred to as a micro lens), inner lens, or the like, and to condense incident light into a light reception portion. Here, as for the optical member, a member having a refracted type lens configuration employing Snell's law is employed.
Note however, with a refracted type lens configuration employing Snell's law, the lens itself is thick, such as around 1 μm or more, so when applying this configuration to the on-chip leans or inner condensing lens of a solid-state imaging device, the device upper layer becomes thick. Thus, undesirable light incidence (referred to as oblique incident light) from adjacent pixels increases, color mixtures due to this oblique incident light increases, and consequently, color reproducibility deteriorates.
Also, existing fabricating processes of on-chip lenses and inner lenses include a great number of processes, such as reflowing resist, and so forth, and are complicated, and are high in costs. In addition, when fabricating such a lens by reflow, only a spherical lens can be fabricated, an asymmetrical lens shape, e.g., deformed in the lateral direction cannot be fabricated.
Further, when reducing the F value of an external image formation system lens, oblique incident light increases, the upper layer becomes thick, so deterioration from ideal sensitivity becomes pronounced, and accordingly, the original sensitivity cannot be obtained (F value light sensitivity deteriorates).
Also, with existing on-chip lenses, condensing efficiency deteriorates depending on an incident angle. That is to say, light entered vertically as to an on-chip lens can be condensed with high efficiency, but condensing efficiency as to oblique incident light decreases. With a solid-state imaging device configured by multiple pixels being arrayed in a two-dimensional manner, in the case of incident light having a spread angle, incident angles differ between a pixel around the center of solid-state imaging device and a pixel on the periphery thereof, and consequently, a phenomenon wherein the condensing efficiency of the pixel on the periphery thereof deteriorates as compared with the pixel around the center thereof, i.e., a phenomenon wherein sensitivity decreases at an end of the device as compared with the center of the device (shading) becomes pronounced.
With regard to deterioration in color reproducibility due to oblique incident light, performing calculation processing for restoring the color reproducibility can be conceived, but may result in a negative effect wherein extra noise is caused, and image quality deteriorates.
Further, when reducing the F value of an external image formation system lens, an F value light sensitivity deterioration phenomenon is caused wherein oblique incident light increases, so the upper layer becomes thick, and deterioration from ideal sensitivity becomes pronounced, and consequently, the original sensitivity cannot be obtained.
On the other hand, as one technique for solving a problem wherein the upper layer becomes thick, and deterioration in sensitivity, an arrangement employing a Fresnel lens has been proposed (e.g., see Japanese Unexamined Patent Application Publication No. 2005-011969 and Japanese Unexamined Patent Application Publication No. 2006-351972).
For example, with the arrangement described in Japanese Unexamined Patent Application Publication No. 2005-011969, an inner condensing lens for further converging light converged on an upper portion lens such as an on-chip lens, and entering this into a photoelectric conversion unit, is configured based on a Fresnel lens. This lens has a feature in that this lens is a refracted type lens, but can be reduced in thickness by being formed as a wave type.
Also, with the arrangement described in Japanese Unexamined Patent Application Publication No. 2006-351972, a condensing element is configured of a combination of multiple zone regions having a concentric configuration which is divided with a line width equal to or smaller than the wavelength of incident light. This has a feature in that the condensing element is configured with a distribution refractive index lens (i.e., Fresnel lens) having a two-step concentric circle configuration as the basis.
Note however, the arrangement described in Japanese Unexamined Patent Application Publication No. 2005-011969 is based on the Fresnel lens concept, and accordingly, this Fresnel lens is a refracted type, so there is limitation in reduction of the thickness thereof as compared with the wavelength order.
Also, in order to fabricate such a wave type requires a process even more complicated than the normal refracted type lens process, further raising costs. Also, only spherical-face lenses can be fabricated, so asymmetry cannot be introduced in designing.
In addition, each arrangement of Japanese Unexamined Patent Application Publication No. 2005-011969 and Japanese Unexamined Patent Application Publication No. 2006-351972 as well, is based on a Fresnel lens, so light obliquely entered in a certain region is not condensed into a point to be condensed originally in some cases (details will be described later). This decreases condensing efficiency, and also causes a color mixture in a case wherein diffused light enters in an adjacent pixel.